void* aPtr = NULL;  // we don't yet know what it points to.
...
aPtr = &height;     // it has the address of height, but no type yet.
...
int h = (int)*aPtr; // with casting, we can now go to that address
                    // and fetch an integer value.

(Learn C Programming; Jeff Szuhay)

'with casting, we can now go [...]'

The question is - can we really?

CodePudding user response：

Dereferencing and Casting Void Ptr (Learn C Programming, Jeff Szuhay)

'with casting, we can now go [...]'

The question is - can we really?

Yes, but the shown code doesn't do any dereferencing. Well, it tries to dereference a void* and cast the result to int. That's not how it should be done. You must first cast to int* and then dereference that int*.

int h = *(int*)aPtr;    // now dereferenced ok (assuming `height` is an `int`)
//      ^   ^
//      |   |
//      |  proper cast
//      |
// dereferencing the right thing